Air balance for impact wrenches



United States Patent 3,407,885 AIR BALANCE FOR IMPACT WRENCHES Martin D. Hoza and Robert A. Pennison, Houston, Tex., assignors to Reed International, Inc., Houston, Tex., a corporation of Texas Filed Mar. 10, 1967, Ser. No. 622,209 5 Claims. (Cl. 17393.6).

ABSTRACT OF THE DISCLOSURE A rotary impact tool is disclosed by the hereinafter specification. The tool housing is provided with forward and rear cavities which are connected by channel for equalizing fluid pressure therebet-ween. In addition, the said tool is provided with atmospheric vents operatively connected to said cavities.

BACKGROUND OF THE INVENTION Field of the invention This invention relates generally to a fluid operated rotary impact tool which initially runs down nuts, bolts, screws or the like and as resistance to such an operation, develops to impart blows to said nuts, bolts, screws and the like to effect a final tightening of same.

DESCRIPTION OF THE PRIOR ART Rotary impact tools of the general type contemplated by this invention are powered by pressurized fluid operated motors. In operation fluid is supplied to a motor cylinder and is used to apply pressure to rotor vanes for the purpose of turning a rotor shaft. It has been noted that notwithstanding the best seals used for con-fining the operating fluid internally of the motor some fluid leaks into the forward and rear portions of the tool housing. The volume of fluid is usually different in each of the portions, and therefore, a pressure differential usually exists between the said portions of the housing. Certain undersirable effects may be directly attributed to the stated pressure differential. For example, lubricants are driven by the pressure differential and as a consequence some internal areas of the tool are lubricant starved whereas other areas are lubricant rich. The said pressure differential may even be sufficient to cause lubricants to be blown out of the tool housing. The force created by the pressure differential also affects the operation of the tool in that it operates as a retarding or staying force against either the thrust or return of the tool hammer depending on the region of high pressure. And, if the high pressure area is in the forward portion of the tool then a thrust is exerted on the tool anvil thereby creating a drag that reduces the effective output power of thetool.

' OBJECTS OF THE INVENTION Accordingly, it is the object of this invention to pro- BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a side sectional view of the preferred ice:

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, an elastic pressure fluid operated impact tool is shown comprising a housing 10 enclosing a rotary vane-type motor 12. The motor is provided with a rotor 14 extending between a front bearing plate 16 and a rear bearing plate: 18. The rotor 14 is provided with shaft ends mounted respectively for rotation in a forward bearing assembly 20 and a rear bearing assembly 22.

The rear bearing plate 18 is an annular shaped member having a bore 24 and a counterbore 25 and is positioned in abutting engagement with the motor 12. The rear shaft end of the rotor 14 is positioned within the bore 24 of the plate 18 while the rear bearing assembly 22 is supported on said rear shaft end within the counterbore 25. The rotor is provided with an inwardly projecting shoulder 26, adjacent the said shaft end, against which is disposed a roller bearing assembly 27 and a compression spring 28. The compression spring extends between the said roller bearing assembly and a Spring cup 30. earl The bearing plate 18, for reasons that will appear, is fixed in position relative to the housing 10 by being secured to an end Wall 34 by a pin 40, and to the motor 12 by a pin 41. The structure of the tool as thus described defines a rear cavity 42 in the counterbore 25 between the bearing assembly 22 and the end wall 34. A similar area generally exists to some extent in all rotary impact tools, and motor fluid tends to leak into this area notwithstanding the best of seals for preventing such leakage. Generally speaking, this fiuid leaks into the space through the junction of the rear bearing plate 18 and the rotor 14. In the present invention, the leakage space or area has been emphasized or enlarged to define the motor leakage fluid cavity 42 as a collecting chamber for said fluid.

The rotor 14 is provided wit-h a central bore 46, a portion of which is splined for the purpose of securing a rotatable hammer 48 therein. The hammer 48 is provided at its forward end with a plurality of lugs '50 which coact with lugs 52 on a rotatably driven anvil 54. The anvil 54 is mounted in a bushing 55 in the forward portion of the housing 10 and is arranged to extend from the housing in the usual manner and is provided with driving flats 56. The anvil is driven by an elongated shaft 58 that extends through the hammer 48 in spaced relation there with and terminates in an enlarged portion which extends into and is pinned to the anvil. The rear end portion of the drive shaft 58 is fixed in a cam assembly of the general type as disclosed and described in the US. patent to Martin D. Hoza No. 3,156,334. The rear end of the shaft 58 is reduced in diameter to provide flats in the cam assembly end, and said end of the shaft extends generally to the aperture 38 in the spring cup 30 in order that lubricants may be introduced therein for the purpose of lubricating the moving and contacting surfaces of the tool.

The housing 10 is bored or otherwise provided with an annular chamber or cavity 62 in the vicinity of the lugs 50 and 52. This cavity defines a forward fluid pocket or chamber for receiving or collecting leakage fluid from the forward end of the motor 12. The said operating fluid in practice leaks out between a forward shaft end 64 of the rotor 14 and the front bearing plate 16. In prior art rotary impact tools of the type described herein, cavities similar to the cavities 42 and 62 exist to some extent 3 whether due to design or not. It is because of their existence and because of the fact that the operating fluid for the air motor leaks or bleeds into these cavities that a pressure differential is created internally of the tool between the two said cavities.

In the described embodiment of this invention, the two cavities are structurally incorporated into the tool design as stated. The housing 10 is provided with a longitudinally extending channel 66 for connecting the two said cavities. As will be obvious from FIGURE 1 of the drawings, the channel 66 communicates directly with the front cavity 62 and extends generally in a straight line longitudinally across the top of housing 10 to the rear bearing plate 18. The rear bearing plate is formed with a port 68, which registers with the cavity 42 and provides communication with the channel 66. The two cavities 42 and 62, being in direct communication with each other will thus allow fluids leaking into them to commingle through the channel 66 and thereby equalize pressure throughout the housing thus eliminating the internal pressure differential between the forward and rear portions of the tool. By eliminating the pressure differential across the tool, the force retaring longitudinal movement of the hammer is eliminated. The very fact of equalized pressure, or that is balanced air, at both ends of the tool allows the lubricant injected through the grease fitting 36 to migrate evenly and naturally throughout the tool and thus allows the even distribution of the said lubricant to all moving parts having surfaces in contact with other parts. The lubricant is thus moved longitudinally in either direction in response to the forces generated by the motor and rotating parts and is unimpeded in the said migration by undesirable internal pressure forces.

The manner in which operating fluid is supplied to the motor 12 is relatively unimportant to this disclosure and any conventional means may be utilized for this purpose. One such means is described in Patent 3,156,334 referred to supra. The said operating fluid is exhausted from the motor 12 through the usual cylinder exhaust ports 71 to a collecting chamber 70 located at the bottom of the motor housing 10. The chamber communicates with an atmospheric exhaust port or vent 72. The motor housing is also provided with a fluid exhaust port 74 which communicates with the forward leakage cavity 62 and the collection chamber 70. In a like manner, a second fluid exhaust port 76 is formed in the motor housing 10 and is used to connect the collection chamber 70 to the rear leakage cavity 42 by means of a port 78 in the rear bearing plate 18. It will thus be apparent that the cavities 42 and 62 are connected to the chamber 70, which in turn communicates with the atmosphere through port 72.

The described exhaust system also eliminates the difference in pressure between the cavities 42 and 62 by effectively placing them at atmosphric pressure. The pressure thus maintained in the forward cavity and therefore, the forward end of the tool is relatively low. Accordingly, the anvil 54 is not subjected to a forward thrust as is the usual case in such tools so that the effective output power of the tool is increased. In addition, by equalizing the pressure in the two cavities with the atmosphere, the aforedescribed undesirable feature of lubricant blowout is effectively eliminated.

Although the foregoing description is necessarily of a detailed character, in order that the invention may be completely set forth, it is to be understood that the specific terminology is not intended to be restrictive or DAVID H. BROWN,

confining, and that various rearrangements of parts and modifications of detail may be restored to without departing from the scope or spirit of the invention as herein claimed.

We claim:

1. A rotary impact tool comprising a housing, an electric pressure fluid operated motor supported within said housing, a hammer rotatably carried by and slidable within said motor, means within said motor to cause said motor to rotate said hammer, said housing having a cavity in the forward portion thereof, a rotatable anvil mounted in the cavity in the forward portion of said housing, means supported in said housing contiguous to the rear of the housing and defining therewith a cavity in the rear portion of the housing, said housing having a channel formed therein communicating with the forward cavity and terminating adjacent the rear of said housing, said means having a passage therein providing communication with said rear cavity and channel to equalize the pressure between the forward and rear portions of said housing and maintain a balanced pressure condition upon the forward and rearward ends of said hammer.

2. An impact tool according to claim 1 wherein said last-mentioned means constitutes a bearing plate for supporting an end of said motor, said plate having a counterbore formed therein which defines with the end of said housing the cavity in the rear portion of the housing.

3. An impact tool according to claim 1 wherein said housing is provided with a fluid collection chamber, a vent connecting said chamber to the atmosphere, a first port connecting said forward cavity to said chamber, and a second port connecting said second cavity to said chamber.

4. An impact tool, according to claim 2, wherein said bearing plate is provided with a port providing communication with said collection chamber and said second cavity.

5. An impact tool comprising a housing, an elastic pressure fluid operated motor, the said housing having fluid passageways communicating with said motor, a rotatable hammer having an enlarged end and a reduced end, the said reduced end being coaxial with and telescoped within said motor, the said enlarged end of said hammer having one or more driving jaws, said housing having a cavity in the forward end and a cavity in the rear end, a rotatable anvil mounted in the forward cavity of said housing, said anvil having one or more driven jaws confronting in said forward cavity with said driven jaws, and elongated passageway formed in said housing and communicating with said cavities to maintain a balanced pressure condition upon said anvil and said enlarged end of said hammer whereby there will be a natural migration of lubricant to all parts of the tool throughout the housing.

References Cited UNITED STATES PATENTS 2,476,632 7/1949 Shaff 173-93.6 3,156,334 11/1964 Hoza 173-936 3,169,585 2/1965 Maurer 173-93 3,175,660 3/1965 Kaman 173-93 X 3,212,590 10/1965 Hoza et al. 173-936 3,253,662 5/1966 Sacchini 17393 X.

Pl'ill'ldl') Examiner. 

